Waterstone's, Britain's biggest book store, has warned it could be left with piles of unsold celebrity autobiographies and cook books in the new year unless sales pick up sharply in the next two weeks.

Seasonal hardback memoirs such as Dawn French's Dear Fatty and That's Another Story by Julie Walters continue to be among festive season best sellers. But Simon Fox, chief executive of HMV Group, which owns Waterstone's, said sales of such titles were lagging behind last year at its 313 book stores.

Fox said that reflected widespread slowing in consumer confidence. Some experts have predicted high street shopper numbers will be down 7.5% in December.

However other booksellers yesterday insisted they had not seen the trends identified by Fox. A spokesman for Asda, where book sales are much more reliant on blockbuster non-fiction titles, said: "Our celebrity books are going very well. [Autobiographies from] Alan Carr and Paul O'Grady have been good for us."

WH Smith, which is promoting celebrity titles in a high-profile TV ad campaign, declined to comment last night.

Fox said: "We've seen a big slowdown in the big non-fiction hardbacks, largely your Christmas celebrity autobiography and cooking books ... Although the quality of the titles is good, we're just not seeing the sales levels we were expecting. The big weeks are ahead of us so it's too early to say what will happen over Christmas. "

Last year titles such as My Booky Wook by Russell Brand, Nigella Express by Nigella Lawson and On the Edge by Richard Hammond dominated Christmas sales for all but the most specialist book retailers. At Waterstone's, such non-fiction blockbusters typically account for more than half of sales during the peak festive period.

According to data provider Nielsen BookScan, UK book sales have slipped 5% since the start of November, having previously been largely unaffected by the economic slowdown. But experts said Nielsen data on individual titles does not appear to show celebrity authors underperforming. Autobiographies from O'Grady and French have sold 450,000 and 350,000 respectively, with books from Walters, Michael Parkinson and Jordan at between 200,000 and 300,000, according to the Bookseller magazine. There are a greater number of celebrity books than last year, a spokeswoman for the magazine said.

Waterstone's warning came after HMV reported comparable sales at the book stores for the 26 weeks to October 25 were down 3.1%, and 1.4% after stripping out the impact of the release of Harry Potter and the Deathly Hallows in 2007.

Fox said HMV stores in the UK and Ireland reported like-for-like sales up 1.6% largely driven by a 23% jump in sales at the Guernsey-based website hmv.com. Finance director Neil Bright said online sales represented between 8% and 9% of the division's revenue, against 6% two years ago and a 20% target for 2010. Fox insisted that the closing down sale at Woolworths would have little impact on HMV. Of greater concern was rapidly devaluing stock mounting up at Entertainment UK, the wholesaling business of Woolworths. Fox is keen to avoid it flooding the market at firesale prices.

"It is not clear what will happen to that stock, other than the longer it sits there the more it degrades. My guess is it will go back to suppliers," he said.